Paving machines are used to deposit layers of asphalt onto a roadway or parking lot bed. A paving machine generally includes a hopper that receives heated asphalt, a screed, and a conveying system that moves the heated asphalt from the hopper onto the bed in front of the screed. The screed is pushed or pulled over the asphalt to level and shape the asphalt into a layer having a desired thickness and width. In some applications, the paving machine is connected to and towed by a dump truck supplying the asphalt to the hopper. In other applications, the paving machine includes a tractor that self-powers the paving machine.
After the asphalt is deposited in a layer of desired thickness and width onto the roadway or parking lot bed, the asphalt is compacted to increase its density and corresponding durability of the finish layer. In some applications, a vibrating mechanism (e.g., a rotating eccentric weight) is connected to the screed to help prepare the asphalt layer for compacting. In particular, the vibrating screed can help align particles in and pre-compact the asphalt, which may help the ensuing compaction process in some applications.
In conventional paving machine configurations, the screed is rigidly connected to a frame of the paving machine, and the vibrating mechanism vibrates the screed and the machine frame together. This, however, increases the mass that the vibrating mechanism is trying to move. As a result, the vibration amplitude of the screed in conventional configurations may be too small to significantly affect compaction. In addition, vibrating the machine frame may cause premature wear or damage to the machine, and may be uncomfortable for the machine operator.
One attempt to improve the effectiveness of a vibrating screed is disclosed in European Patent No. 586,886 of Ulrich that published on Aug. 5, 1993 (“the '886 patent”). Specifically, the '886 patent discloses an asphalt paver having a chassis, a central drive unit connected to propel the chassis, a hopper mounted to the chassis, and a conveyor device that conveys paving material to a rear of the paver. A screed assembly is attached to the chassis at the rear of the paver, and includes a main screed and extendable auxiliary screeds. Each of the main and auxiliary screeds includes a screed body coupled with the chassis, a screed plate connected to the body, a vibrator connected to the screed plate, and a decoupling device connected between the screed body and the screed plate. The decoupling device can embody a spring or a rubber block, and functions to vibrationally isolate the screed plate from the screed body. This elastic decoupling of the screed plate from the screed body and the remainder of the paver lowers a mass moved by the vibrator and allows for increased vibrational amplitude of the screed plate.
Although the paver of the '886 patent may improve compaction and grain alignment performed by a screed plate, the paver may still be less than optimal. Specifically, it may be important for the screed plate to remain flat throughout operation in order to form a flat surface in the asphalt layer. And connecting the vibrator directly to the screed plate may cause warping, twisting, or other deformation of the screed plate that can negatively affect the asphalt layer. In addition, the '886 patent does not disclose a way to tune a deformed screed plate.
The disclosed paving machine and screed assembly are directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.